On Fri, Apr 16, 2021 at 04:00:37PM +0800, Jeffle Xu wrote:
> Hi,
> How about this patch to remove the extra poll_capable() method?
>
> And the following 'dm: support IO polling for bio-based dm device' needs
> following change.
>
> ```
> + /*
> + * Check for request-based device is remained to
> + * dm_mq_init_request_queue()->blk_mq_init_allocated_queue().
> + * For bio-based device, only set QUEUE_FLAG_POLL when all underlying
> + * devices supporting polling.
> + */
> + if (__table_type_bio_based(t->type)) {
> + if (dm_table_supports_poll(t)) {
> + blk_queue_flag_set(QUEUE_FLAG_POLL_CAP, q);
> + blk_queue_flag_set(QUEUE_FLAG_POLL, q);
> + }
> + else {
> + blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
> + blk_queue_flag_clear(QUEUE_FLAG_POLL_CAP, q);
> + }
> + }
> ```
Frankly speaking, I don't see any value of using QUEUE_FLAG_POLL_CAP for
DM, and the result is basically subset of treating DM as always being capable
of polling.
Also underlying queue change(either limits or flag) won't be propagated
to DM/MD automatically. Strictly speaking it doesn't matter if all underlying
queues are capable of supporting polling at the exact time of 'write sysfs/poll',
cause any of them may change in future.
So why not start with the simplest approach(always capable of polling)
which does meet normal bio based polling requirement?
Thanks,
Ming
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